The Mass Spectrometry (MS) Shared Resource offers a wide range of analytical capabilities to support the needs of UTHSCSA investigators and others in the nearby research community. The core facility is directed by Susan T. Weintraub, Ph.D., and is located on the main UTHSCSA campus. The facility includes the following instrumentation: 1) Finnigan LCQ ion trap mass spectrometer capable of nanospray and micro-HPLC-ESI/MSn measurements, used in conjunction with a Michrom BioResources MAGIC 2002 micro-HPLC; 2) Applied Biosystems Voyager DE-STR MALDI-TOF/MS; 3) Applied Biosystems Voyager Elite MALDI-TOF/MS; and 4) Finnigan SSQ700 quadrupole mass spectrometer which is able to perform GC/MS and direct probe analyses using electron impact and chemical ionization with positive and negative ion detection. A satellite facility of the MS Core has been established at the Institute of Biotechnology within the Texas Research Park, which is located 20 miles from the UTHSCSA main campus. The satellite unit encompasses a 200 sq. ft. laboratory and includes the following instrumentation: 1) an Applied Biosystems Voyager DE-PRO Biospectrometry workstation, consisting of a high performance integrated MALDI-TOF mass spectrometer, a SymBiot I Sample Workstation, and a PS-1 sample handling and data analysis system; and 2) a Thermo Finnigan integrated LC/MS system consisting of a Surveyor HPLC coupled in-line with a Finnigan LCQ DUO ion trap mass spectrometer with MS/MS capability. Major services provided to SACI investigators by the MS Shared Resource include: molecular mass determination; protein identification from solution or polyacrylamide gel; sequence analysis; elucidation of sites of post-translational modification, focusing on phosphorylation. Detection limits in the sub-picomole range are routinely obtained, making it possible to realistically characterize proteins and peptides isolated from biological samples.